Pulse forming network



Feb. 26, 1952 w. R. AIKEN PULSE FORMING NETWORK 2 SHEETS-SHEET 1 Filed April 28, 1950 i R m E wJ m P006 M6 A L R 00 m4 w m A It MW m W R m3 D LIMITER I INVENTORL WM. R055 A IKEN A TTORNEX PatentedFeb. 26, 1952 UNITED STATES PATENT OFF-ICE 2,587,421; PULSE FORMING NETWORK Claims.

mined frequency according to the direction of frequency shift.

The increasing use of frequency modulated electrical systems requires auxiliary circuits for control purposes. Certain applications of such systems require the development of a controlpulse :of "voltage at a predetermined frequency when the frequency shift is in a particular direction. An example of the above-referenced systems is a frequency modulated cyclotron wherein the accelerating potential :applied is frequency modulated. With such a cyclotron the timing of the operation may be readily based upon the frequency of the frequency modulated accelerating voltage during each frequency excursion and is simplified thereby. With an appropriate control circuit it is possible to properly time the initiation of the particle injection and of thedefiector voltage. The present invention. provides an electronic control circuit for forming a pulse of voltage having the required characteristics in a simple manner utilizing standard electronic parts .well within theirzratings.

It is therefore an object of. the present invention to provide a new andimprove'cl pulse forming controlnetwork.

Another object of the present invention i .to provide a pulse formingcontrol network, the output of which occurs at a predetermined frequency when the frequency shift of a frequency modulated signal voltage is in a particular direction.

Still-another object of the present invention is to provide a pulse forming control network that will develop an output signal which is'dependent only on frequency and on the direction of frequency shift of a frequency modulated input voltage and which is independent ofamplitudemodulationand extraneou interference.

.Afurther object of the presentinventi-on is to provide a pulse forming control network which is. not criticalin the formation of an output signal at the gatecircuit therein.

Other objects and advantages will be apparen in the followingdescription and claims considered together with the accompanying drawing, in which:

Figure 1 is a block diagram illustrating the presentinvention,

Fig. 2 is aseries of time correlatedvoltage waveforms. which. occur at various elements durin operation of the present invention, and

Fig. 3 is a schematic wiring diagram of the present invention.

Referring to the drawing in detail, and to Figs. 1 and 2 in particular, an input terminal I0 connects a frequency modulated voltage, as shown in Fig-. 2A, to a limiter 20. The limiter 20 removes any variations in the envelope of the frequency modulated voltage and ha an output voltage, as shown in Fig. 2B, which is connected to the input of a discriminator 30. The output voltage of the discriminator 20 varies substantially sinusoidally about a predetermined frequency, as shown in Fig. 2C, and is connected to the input of an integrator 40 and an amplifier 50. A voltage, as

show-n in Fig. 2D, having the same general waveform as theinput, but shifted somewhat in phase, appears at the output of the integrator 40 and is then impressed upon an amplifier 60. Since the output voltage, as shown in Fig. 2E, of the amplifier is inverted with respect to the input thereto, an inverter I0 is connected to such output to reestablish the original phase relationship, as shown in Fig. 2F. The latter voltage is then impressed on one input of a gate 80. A second input of the gate is connected to the output of the amplifier 50 and obtains a voltage therefrom having a waveform as shown in Fig. 2G. For convenience the waveforms at the inputs of the gate 80 have been included on a single line, as shown in Fig. 2H. The output of the gate 80 is a pulse of voltage, as shown in Fig. 2J,, occurring at the time both input voltages are negative, and appears at an output terminal 90.

Referring now to Fig. 3, an input terminal IOI carries a frequency modulated signal voltage, as shown in Fig. 2A, impressed from a source (not shown), such as the accelerating voltage supply of a frequency modulated cyclotron. A pentocle tube I02, which'serves as a limiter tube to remove any amplitude modulation from the signal voltage, is connected with the control grid to the terminal It] through a series connected current limiting resistor I03 and a coupling condenser I04. The junction between the terminal IOI and the condenser I04 is connected to a :ground connection I06 through a resistor I01. The junction between the condenser I04 and the resistor I03 is connected to the ground connection I06 through a biasing resistor I00. To complete'the 'cormectionsfor the tube I02, the cathode is directly connected to the ground connection I06, the screen grid is connected to the ground connection through a by-pass condenser E09 and to one end of a resistor III, the suppressor grid is directly connected to the cathode, and the anode is contion between condensers 3 nected to a resonant tank circuit H2 comprising two parallel connected variable condensers H3 and H4 and the primary winding H6 of a coupling transformer H1. The transformer H1 is provided with an adjustment H8 for changing the permeability of the core and thereby the values of the inductance of the windings. One side of the tank circuit H2 is connected to the junction between the screen grid of the tube I02 and the resistor III so that the primary winding of the transformer H1 provides a direct current path to the anode of the tube. To supply the necessary anode voltage to the tube I02 the other end of the resistor H I is connected to junction I2I of a voltage divider I22 comprising a series connected resistor I23, resistor I24, and potentiometer I25. The voltage divider I22 is in turn connected to a pair of terminals I21 and I28, one of which is common to the ground connection I06 and the other of which carries a positive unidirectional voltage from an external source (not shown). The secondary winding I3I of the transformer H1 is connected in parallel withtwo series connected condensers I I32 and I33, the junction between which iscoupled to the anode of the tube a condenser I34.

I02 through Connected in parallel with the condensers I32 and I33 is a variable condenser I36, the latter being gang controlled along with the condenser H3. Thus it will be readily apparent that the secondary winding I3I and the condenser I36 form a second resonant tank nal of another rectifier I42, also preferably of the crystal type. Another voltage divider comprising two series connected resistors I43 and I44 is connected between the negative terminals of the rectifiers MI and I42. Two series connected condensers I46 and I41 are also connected to the negative terminals of the rectifiers MI and I42. discriminator circuit being described the junc- I46 and I41 is connected to the junction between the resistors I43 and I44, and to the junction between the resistors I38 and I39. Further, the negative terminal of the rectifier I42 is connected to the ground connection I06 so that the entire output voltage of the discriminator circuit is above the ground potential. The values of the To complete the connections of the elements comprising the discriminator circuit,"

just described, arepreferably chosen to a narrow frequency band response to permit rapid voltage versus frequency variations, but still broad enough to pass the desired pulse;

To complete the connections of the tube I5I the cathode is connected to the ground connection I06 through a parallel connected resistor I53 and by-pass condenser I54 and the anode is connected to the positive terminal I28 through a dropping resistor I56. The output ofthediscriminator circuit is also connected to an intetrol grid of a triode amplifying tube I6I.

tor I84.

grating circuit comprising a series resistor I51 and condenser I58, one side of the latter being connected to the ground connection I06. The values of the resistor I51 and condenser I58 are chosen to cause a phase shift in a lagging direction between the input voltage and the voltage across the condenser I58. To amplify the shifted output voltage the junction between the resistor I51 and condenser I58 is connected to the con- Other connections of the tube I6I are from. the cathode to the cathode .of the tube I5I and from the anode to the terminal I28 through a dropping resistor I62. The anode of the tube I6I is also connected to the control grid of a tube I66 through a coupling condenser I61, the latter tube I66 serving as an inverter for the amplified voltage appearing at the anode of the former tube I6I. To complete the connections for the tube I66 the control grid is connected to the ground connection I06 throughv a biasing resistor I68, the cathode is connectedto the ground connection I06 through a parallel connected resistor HI and condenser I12, and the anode is connected to the terminal I28 through a dropping resistor I13.

The inverted signal appearing at the anode of the tube I66 is coupled to the control grid of a triode tube I16 through a series connected coupling condenser I11 and current limiting resistor I18. The junction between the condenser I11 and the resistor I18 is connected to the cathode of the tube I16 through a biasing resistor I19. The amplified signal appearing at the anode of the tube I5I is coupled to the control grid of another triode tube I8I through a series connected coupling condenser I82 and current limiting resistor I83. The junction between the condenser I 82 and resistor I83 is connected to the ground connection I06 through a biasing resis- The tubes I16'and I8I are interconnected in the form of a gate circuit preferably to develop an output voltage only when'the control grids of both tubes become negative. To accomplish such a result the anode of the tube I16 is connected to the anode of the tube I8I and the cathodes are similarly connected together. The cathodes of the tubes I16 and I8I are further connected to the ground connection I06 through a by-pass condenser I86 and to the adjustable element of the potentiometer I25. The anodes of the tubes I16 and I8I are connected to the positive terminal I 28 through a dropping resistor I81. To limit the output voltage at the anodes of the tubes I16 and I8I a connection from the anodes is made to the positive terminal 'ofa rectifier I88, preferably of the crystal type,

the negative terminal of which is connected through a resistor I89 to theadjustable element of a potentiometer I9]. The potentiometer is connected between the positive terminal I28 and the ground connection I06 and the portion of the voltage appearing between the adjustable element and the ground connection I06 is bypassed by a condenser I92 connected therebetween. The junction between the rectifierl88 and the resistor I89 is connected to an output terminal I96 which serves asa convenient means for connecting to an external circuit. Other external connections are provided by connecting the ground connection I06 to an input terminal I91 and an output terminal I98.

Consider now the operation of the foregoing described circuit with the terminals I21 and I28 suitably connected to an energized source of unidirectional voltage and with the input terminals IBI and I91 connected across a source of frequency modulated signal voltage having a waveform, as shown in Fig. 2A. As stated previously the tube I02 is connected in the form of a limiter and serves to remove any amplitude modulation which might be present in the incoming signal voltage. The condenser H3 provides a coarse adjustment of the resonant frequency of the tank circuit II2, while the condenser II4 provides a fine adjustment. Also provided to adjust such resonant frequency is the permeability adjustment H6 of the coupling transformer II1. With the values of the tank circuit set for a certain predetermined resonant frequency within the range of frequency of the frequency modulated signal voltage, the impedance of the tank circuit I-I2 varies from a maximum value to a minimum value as the frequency approaches such resonant frequency and increases to a maximum value again as the frequency continues to increase. It will 'be'readily apparent that each time the frequency modulated signal voltage makes an excursion from a minimum value to a maximum value and back again to the minimum value, the resonant frequency of the tank circuit II 2 will be passed twice, once during the ascending swing of the frequency, and once during the descending swing of the frequency. The values of inductance of the secondary winding I3I andthe capacitance -the condenser I34, the rectifiers MI and I42, the

resistors I43 and I44 as interconnected, is the "same as occurs in any conventional discriminator circuit to produce a substantially symmetrical sine wave each time the frequency of the input voltage passes through the resonant frequency of the tank circuits H2 and I31. On the rising frequency the voltage at the junction between the resistor I43 and rectifier I4I increases positively from zero to a maximum, decreases to zero at a time correlating to the time of the resonant frequency, then decreases to a maximum negatively, and finally back to zero. Similarly, during decreasing frequency a voltage is developed which increases negatively from zero to a maximum, increase positively to zero at the resonant frequency, then continues toxincrease to a positive maximum and finally returns to zero. These latter two voltage waveforms are illustrated in Fig. 2C, and are impressed at the control grid of the amplifier tube I5I and at the input to the integrator comprising the resistor I51 and condenser I56. The values of the resistor I51 and condenser I58 are chosen to shift the phase of the output voltage, as taken across the condenser I58, with respect to the input voltage thereto, and as will be pointed out hereinafter such values are not critical nor is the degree of phase shift. The voltage across the condenser I58, as shown in Fig. 2D, is then impressed upon the control grid of the amplifier tube I6I. For the purpose of the presently described embodiment of the invention, it is necessary to invert the voltage, as shown in Fig. 2E, appearing at the anode of the tube I6I, therefore such voltage is coupled to the control grid of a second amplifier tube I66. The voltage at the anode of the tube I66, as shown in Fig. 2F, is connected to the control grid of one tube I16 of a pair of tubes I16 and I8I which are interconnected in the form of a gate to develop an output voltage only at the time both tube are nonconducting. The voltage at the anode of the tube I5I, as shown in Fig. 2G, is connected to the control grid of the tube I8I. With the tube I16 normally biased so that the tube is conducting and the tube I8I normally biased so that the tube is nonconducting, the impression of a positive bias at the control-grid of the tube I16 will have no effect on the operation of the gate. Similarly a positive voltage applied to the grid of the tube I8I will render that tube conducting, but no output voltage will be developed. It is also to be noted that no output voltage is developed when voltages applied to the grids of the tubes I16 and I8I render the normally conducting tube nonconducting and the normally nonconducting tube conducting. As stated previously, it is desirable to obtain "an output voltage when both tubes are rendered nonconductin'g, and as will be seen in Fig. 2H such condition exists only during the descend ing frequency of the frequency modulated signal voltage at a time corresponding to the occurrence of the resonant frequency of the tank circuits H2 and I 31. Such output voltage then is shown in Fig. 2J along with its time correlation to the other waveforms shown in Fig. .2. 1

From the foregoing it is readily apparent'itha the objects of the present invention have been accomplished in the proposed manner. From a frequency modulated input voltage :an output voltage pulse has been developed which is initiative at a predetermined frequency and, as desired, during the time the frequency is decreasing.

It is to be noted that by minor modifications in the circuit that the output voltage may be-developed during the time the frequency is .increasing. Such modifications merely involve coupling the anode of the tube 'I6I to thecontrol grid of the tube I16, coupling the anode of the tube I5I to the control grid of the tube I6.6,:and coupling the anode-of the tube I66 to the control grid of the tube I8I. These changes are sufficient to make the controlgrids .of thetubes I16 and I8I negative at the time of the desired frequency while the frequency is increasing.

It is also to be noted that .a differentiator zcircuit may be substituted for the integrator described above. However, such a change results in a-more critical circuit in that the degree of phase shift has to be exactly ninety degrees for proper operation and allows, the generation of a spurious output voltage pulseby theoccurrence of a positive noise pulse within the circuit.

While the present invention has been described in detail with respect to one embodiment it will, of course, be apparent that numerous modifications may be made within the spirit and scope of the invention and it is therefore not desired to limit the invention to the exact details shown except insofar as they may be defined in the following claims.

What is claimed is:

1. In a pulse forming control circuit for a frequency modulated system, the combination comprising a discriminator having a pair of tank circuits tuned to a predetermined frequency for developing a substantially sinusoidal voltage each time said predetermined frequency occurs, means amplifying said sinusoidal voltage to form a first signal voltage, integrating means shifting the phase of said sinusoidal voltage to form a second signal voltage lagging said first signal voltage in time, means amplifying said second signal voltage, means inverting said amplified second signal voltage, and gate means responsive only to the occurrence of a negative amplified first signal voltage and a simultaneously negative'inverted second signal voltage to initiate a positive output voltage at said predetermined frequency.

.2. In a pulse forming control circuit for a frequency modulated system, the combination comprising an input connected to said system for receiving a frequency modulated voltage therefrom, limiting means connected to said input for removing amplitude modulation from said frequency modulated voltage, discriminating means connected to said limiting means for developing second signal voltage lagging said first signal voltage in time, amplifying means connected to said integrating means, inverting means connected to said amplifying means for changing the phase of said amplified second signal voltage by 180 degrees, and gate means having two inputs and an2 output for initiating a positive voltage at said .output when both inputs are impressed nega- "tively. one of said inputs being connected to said first signal voltage amplifying means and the otherof said inputs being connected to said second signal voltage inverting means.

3. In a pulse forming control circuit for a frequency modulated system, the combination comprising an input connected to said system for receiving a frequency modulated voltage therefrom, limiting means connected to said input for removing amplitude modulation from said frequencymodulated voltage, discriminating means connected to said limiting means for developing a substantially sinusoidal voltage each time saidfrequency modulated voltage passes through a predetermined frequency, amplifying means con nected to said discriminating means for forming a first signal voltage, a series connected resistor and condenser connected to said discriminatingmeans, the values of said resistor and condenser being predetermined so that the voltage across said condenser lags said sinusoidal voltage to form asecond signal voltage, amplifying means connected to the junction between said resistor;-

and: condenser for amplifying said lagging sec ond signal voltage, inverting means connected to said amplifying means for changingthe phase of said amplified second signal voltage by degrees, and gate means having two inputs and an output for initiating a positive voltage at said output when both inputs are impressed negatively, one of said inputs being connected .to' said first signal amplifying means and the other input being connected to said second signal voltage inverting means.

4. In a pulse forming circuit for a frequency modulated system, the combination comprising an input connected to said system for receiving a frequency modulated voltage therefrom, limiting means connected to said input for removing amplitude modulation from said frequency modulated voltage, discriminating means connected to said limiting means for developing substantially sinusoidal voltage each time said frequency modulated voltage passes through a predetermined frequency, amplifying means connected to said discriminating means for forming a first signal voltage, integrating means connected to said discriminating means for shifting the phase of said sinusoidal voltage to form a second signal voltage lagging said first signal voltage in time, amplifying means connected to said integrating means, inverting means connected to said amplifying means for changing the phase of said amplified second signal voltage by 180 degrees, and a first and second triode vacuum tube, means for applying operating voltages between the anode and cathode of each of said tube said tubes having the anodes and cathodes interconnected, means for biasing the control grid of said first tube positively, means for biasing the control grid of said second tube negatively, means for coupling said inverted second signal voltage to the control grid of said first tube, and means for coupling said amplified first signal voltage to the control grid of said second tube.

5. A pulse forming control circuit of claim 1, wherein the integrating means comprises a series-connected resistor and capacitor with said second signal voltage being formed across the capacitor.

WILLIAM R. AIKEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,190,504 Schlesinger Feb. 13, 1940 2,475,074 Bradley et a1 July 5, 1949 2,484,612 Dehn et a1 Oct. 11, 1949 2,501,368 White Mar. 21, 1950 

